Provide dynamic and static pointer casts in pcl namespace to allow easy migration from boost to std smart pointers

[aPonza]

Stems from #3750.

[kunaltyagi]

Based on the CI, I'd say that we need pcl::*_cast.

error: 'dynamic_pointer_cast' was not declared in this scope

[Morwenn]

If I'm not mistaken ADL does not work here because smart pointer casts are function templates taking an explicit template parameter - this was fixed in C++20 but you have to workaround it in earlier standard versions.

You can work around it by first making one of the names visible to the compiler in scope, then ADL should work properly:

boost::shared<U> ptr;
using std::dynamic_pointer_cast; // The compiler sees a function template and considers that unqualified `dynamic_pointer_cast` has to be resolved as a function name/overload set
auto ptr2 = dynamic_pointer_cast<T>(ptr); // ADL is performed, boost::dynamic_pointer_cast is found despite std:: being used to make the name visible

Sprinkling using std::*_cast; should be enough without having to introduce PCL-specific functions. Now introducing functions also avoids having to rely on this specific form of ADL and lets you write one line instead of two.

[kunaltyagi]

LGTM

[kunaltyagi]

Just waiting for another set of eyes before merge.